In a display device for displaying color images, one pixel comprises a plurality of sub-pixels, and expresses various colors by causing the sub-pixels to output light of different colors. In this display device, to display an image with a high luminance, it is necessary to increase, for example, the luminance of a backlight, which may increase consumption of power. In order to improve this, there is a technique of adding a white sub-pixel to general red, green and blue sub-pixels. Addition of the white sub-pixel increases the entire luminance, and hence can reduce the luminance of the backlight, with the result that consumption of power can be reduced.
In general, data input to the display device comprises input values of red, green and blue colors. When the white sub-pixel is added to a pixel, it is necessary to generate an output value for the white sub-pixel, based on the input values, and also to generate output values for the sub-pixels of the red, green and blue colors. Thus, the processing load of image display is increased.